Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$37.26	7.458%	$40.0389	$40.04	$40.05	$40.00
Purchase #2	$138.64	5.767%	$146.6354	$146.64	$146.65	$146.60
Purchase #3	$101.71	4.765%	$106.5565	$106.56	$106.55	$106.60
Purchase #4	$55.71	10.287%	$61.4409	$61.44	$61.45	$61.40
Purchase #5	$63.77	12.111%	$71.4932	$71.49	$71.50	$71.50
Purchase #6	$19.41	10.493%	$21.4467	$21.45	$21.45	$21.40
Purchase #7	$68.96	12.212%	$77.3814	$77.38	$77.40	$77.40
7 purchase totals =	$485.46		$524.9930	$525.00	$525.05	$524.90